Drive devices and drive control units of the type described above are generally known. The drive control units generally take the form of motion control devices, in particular as numerical control units for machine tools or motion control units for production machines. The sequences of setpoint values that are communicated from the drive control units to the corresponding drive devices are generally sequences of position- or rotational speed setpoint values. In individual cases, however, the determination of torque- or other setpoint values is also possible.
The drive devices are conventional motor control devices. They convert the determined position-, rotational speed-, torque- or other setpoint values at least into current setpoint values. In many cases, the drive devices themselves directly trigger their electric motors. In other cases, they communicate the current setpoint values to a lower-level device, which effects determination of the trigger signals for circuit-breakers and triggering of the circuit-breakers.
During normal operation the drive device carries out only the conversion of the communicated sequence of setpoint values into the current setpoint values but does not carry out any monitoring tasks with regard to the electric motor. In many operating states, however, it is necessary for the electric motor to be controlled in a specific manner and also monitored. For example—depending on the operating situation—one of the following requirements may exist:                The electric motor is to be decelerated to zero rotational speed and then actively held at a standstill.        The rotational speed of the electric motor is to be lowered until it is below a maximum permissible rotational speed.        The motor is to be operated only in a specific direction of rotation. This mode of operation may be important particularly if there is a risk of a so-called pull-through load.        The motor is to be operated at most with a torque limit.        The electric motor is to be brought to a standstill and then de-energized. Optionally an interaction with a mechanical brake may occur.        
Other requirements may also exist.
Such monitoring operations are conventionally carried out by the drive device. If the electric motor in the monitoring mode of the drive device does not comply with the required operating condition, it is disconnected from the power supply by the drive device. A braking device, in particular a mechanical brake, may possibly also be actuated.
Whether the electric motor is to be monitored by the drive device and the possible nature of the monitoring is decided by the drive device on the basis of corresponding safety-related signals that are supplied from outside to the drive device. Parameters that more closely define the state to be monitored may also be supplied from outside to the drive device. Thus for example the maximum permissible rotational speed value, the desired direction of rotation or the maximum permissible torque value may be supplied to the drive device.
From the above, purely exemplary list of monitoring operations it is clear that for many monitoring operations the electric motor even after initiation of the monitoring mode may continue to remain connected to the power supply. In the framework of the present invention only such states are of importance. So long as in such monitored states the actual value of the electric motor complies with the actual-value condition, the electric motor remains connected to the power supply and is operated in accordance with the current setpoint values determined by the drive device. It is only if the electric motor breaches the actual-value condition that the drive device automatically causes the electric motor to be disconnected from the power supply. The drive device—speaking metaphorically—pulls the emergency brake.
Within the framework of selection of the setpoint values by the drive control unit, as a rule a management of the electric motor occurs. The time sequence of setpoint values is therefore determined by the drive control unit while simultaneously taking into account the dynamics of the electric motor—possibly also while taking into account a load actuated by the electric motor—in such a way that the electric motor may follow the corresponding setpoint selection. If the monitoring mode is initiated, the appropriate information therefore generally has to be supplied not only to the drive device but also to the drive control unit. In the prior art various procedures for this purpose are known.
Thus for example it is known to transmit the first signals via a fail-safe programmable controller to the drive device. In this case, three embodiments are known.
Firstly, it is known for the first signals to be communicated by the fail-safe programmable controller not only to the drive device but also to the drive control unit. Secondly, it is known for the drive control unit alternatively passively to listen in on the data traffic from the fail-safe programmable controller to the drive device. Thirdly, it is possible for the drive device to output the first signals and for the first signals to be supplied via an intrinsic terminal module directly to the drive control unit. This means that this supplying has to be effected in addition to the supplying of the first signals to the drive device.
It is further known for the first signals to be supplied directly via a terminal module to the drive device. In this embodiment it is known to associate an intrinsic terminal module with the drive control unit. The signals supplied to the drive control unit may in this case alternatively directly be the first signals or signals for output that are determined by the drive device on the basis of the first signals.